Technical Abstract:
In the Midwestern United States, herbicide transport in surface waters represents one of the major impacts of agriculture on the environment. Soil-applied, preemergent herbicides are present during late spring to early summer in nearly every major river basin in the Midwest. The factors affecting herbicide transport in surface water are a function of the specific chemical properties of the herbicide and their interaction with soils, climate, and land-use (i.e., compound usage and management practices). The relative importance of these factors to herbicide transport changes with scale. Concentration and mass flux data of atrazine, alachlor, and metolachlor, which have been monitored in northern Missouri for the past several years at all three scales, will be presented. In addition, the importance of metabolite transport and their contribution to the total mass flux of atrazine at the watershed and basin scales will be discussed.